This invention relates generally to gas turbine engine front frames and more particularly, to articulated fan front frames for gas turbine engines.
Gas turbine engines include a fan front frame that channels airflow entering the turbine engine downstream into the core engine. At least some known gas turbine engines include articulated inlet guide vane assemblies that extend substantially circumferentially within the engine. Each inlet guide vane assembly includes a fixed strut and a variable flap that is coupled downstream from the strut.
The flaps are variably positionable during engine operation to facilitate improving engine performance over a wide range of engine operations. More specifically, as the engine is operated at design operating conditions, the flaps are generally axially aligned with respect to each respective strut. An orientation of the flaps is determined by the design of the engine and the conditions at which the engine is operated. During off-design operating engine conditions, the flaps are rotated to a closed position to selectively control an angle at which incoming airflow impinges a first row of blades of a downstream compressor.
To facilitate optimizing engine operating efficiency and stability, it is important that a smooth airflow transition occurs through the inlet guide vane assembly and immediately downstream thereof at all engine operating conditions. However, in at least some known inlet guide vane assemblies, certain rotational orientations of the flap may generate turbulence in the airflow downstream from the flap. Such turbulence may cause a non-integral rotor blade vibration known as xe2x80x9cflutterxe2x80x9d and/or high airfoil stresses in the blades of the fan immediately downstream of the inlet guide vanes. More specifically, air flowing past an inlet guide vane assembly has a tendency to flow from a pressure side of the flaps to a suction side of the flaps. The flow of air between the strut and the flap can cause separation of the airflow from the suction side of the inlet guide vane assembly, which may introduce turbulence into the airflow entering the fan blades. Continued engine operation with flutter may damage a fan blade, shorten its useable life, or restrict operation of the engine.
In one aspect, a method for assembling an articulated fan front frame for a gas turbine engine is provided. The method comprises forming a strut including a pair of sidewalls connected at a leading edge and a trailing edge, forming a flap including a first sidewall and a second sidewall connected at a leading edge and a trailing edge, and extending in radial span between a root endwall and a tip endwall, wherein each endwall extends between the first and second sidewalls, and wherein at least one of the root endwall and the tip endwall is contoured in a radial direction extending between the flap leading and trailing edges, and pivotally coupling the flap downstream from the strut such that a gap is defined between the flap and the strut.
In another aspect, a fan front frame assembly for a gas turbine engine is provided. The fan front frame assembly includes at least one articulated inlet guide vane sub-assembly including a strut and a flap that is downstream from the strut. At least one of the strut and the flap is variable positioned during engine operation. The flap includes a first sidewall and a second sidewall connected at a leading edge and a trailing edge, and extends in radial span between a root endwall and a tip endwall. Each flap endwall extends between the first and second sidewalls, and at least one of the root endwall and the tip endwall is radially arcuate between the flap leading and trailing edges.
In a further aspect, a gas turbine engine that is operable between design and off-design conditions is provided. The engine includes a fan front frame assembly including at least one articulated inlet guide vane sub-assembly that is configured to channel airflow entering the engine downstream. The inlet guide vane sub-assembly includes a strut and a flap that is downstream from the strut. The flap includes a pair of sidewalls that are connected at a leading and a trailing edge, and extend radially between a tip endwall and a root endwall. At least one of the tip endwall and the root endwall extend between the pair of sidewalls and are contoured in a radial direction between the flap leading and trailing edges.